Evaluation of potential exposure-related effects on male fertility is problematic. Semen samples are difficult to obtain in industrial surveillance programs and quality measures (sperm counts and motility) are highly variable within subjects and between fertile and infertile men. Recent studies have demonstrated that serum levels of Inhibin B, a Sertoli cell secretory protein, are suppressed in the presence of testicular injury in animals or men. This protein marker appears to have less variability than serum FSH levels and the measures of semen quality. At the present time, serum Inhibin B levels have not been used to evaluate potential testicular injury due to occupational exposures to male reproductive toxins. Our primary objective is to determine whether measurement of serum Inhibin B levels is a useful surveillance tool for the detection and prevention of exposure-related testicular toxicity in the industrial setting. The study will use stored, frozen serum specimens obtained from workers at a synthetic resin production facility over the past two decades. Specimens from compounding workers (exposed to lead and phthalate esters) and synthetic rubber production workers (exposed to acrylonitrile, butadiene, and styrene) will be analyzed for Inhibin B and FSH levels and compared with those from an age-matched control group (non-exposed administrative workers). The specific aim is to determine whether exposure to reproductive toxins results in suppression of Inhibin production. A random group of samples from the all facility workers will also be analyzed for Inhibin B and FSH. Using a case-control approach, exposures profiles of workers with suppressed Inhibin B levels will be compared to those with normal levels using recent and cumulative exposure measures. The aim of the case control study is to determine whether serum Inhibin B suppression is associated with specific chemical exposures. Finally, the study will assess whether serum Inhibin B levels are predictive of future fertility or infertility, using data obtained in annual medical histories of the workers. We believe that this investigation is novel and has the potential to be the foundation for meaningful medical surveillance for male reproductive toxicity.